As it turns out, the benefits of breast milk aren’t just found in the milk itself: There are also benefits in establishing contact between a mother’s skin and her baby. Researchers observed 107 mother-child pairs, and they found that 30 percent of the beneficial bacteria found in a baby's intestinal tract comes from breast milk itself, while another 10 percent comes from the contact with the skin of a mother's breast. Previous studies have linked good intestinal bacteria to improved immune function, which makes this finding even more significant.

According to the researchers, this effect doesn't just occur in babies who are exclusively breastfed—breast milk that's consumed after children start eating solid food holds this protective effect as well.

This doesn't mean babies who are not breastfed are necessarily less healthy than those who are—this particular study didn't observe formula-fed babies—but it shows us another intriguing plus side to breast milk. The researchers will be studying this topic in greater detail, in the hopes of discovering which components of breast milk are responsible for this benefit.

"Breast milk is this amazing liquid that, through millions of years of evolution, has evolved to make babies healthy, particularly their immune systems," senior study author Grace Aldrovandi said, according to a UCLA release for the news. "We're appreciating more and more how these bacterial communities—particularly in the intestine—help guard against the bad guys. We know from animal model systems that if you get good bacteria in your gut early in life, you're more likely to be healthy."